Preparation Of Dielectric Foam With High Dielectric Constant And Low Dielectric Loss Polymer

Luneberg lens antenna is a spherically symmetric dielectric antenna,which has the characteristics of high gain,low sidelobe and broadband.It can realize multi beam and large angle scanning.It is mainly used in satellite communication,electronic countermeasure and other fields.However due to its large volume,heavy weight and the difficulty in fixing spherical structure,it is greatly limited in practical application.Therefore,in view of the demand of new lightweight dielectric composites for radar communication,it is of practical significance to carry out the research of high dielectric properties composites.Although a large number of literatures have studied high dielectric composites,there are still some problems in preparation of polymer dielectric foams with low density and low dielectric loss.In this paper,high dielectric ceramic/polymer system and conductive filler/polymer system were constructed to prepare high-dielectric composite materials,and then corresponding polymer dielectric foams were prepared by carbon dioxide supercritical fluid foaming process.Three main works were done.1、The silane coupling agent KH550 was used to modify the surface of barium titanate nanoparticles,and the composites were prepared by physical blending with polypropylene.Polymer dielectric foam was prepared by physical foaming with carbon dioxide.The results showed that KH550 could effectively improve the interfacial compatibility between barium titanate and polypropylene,and the interfacial polarization strength was enhanced.Compared with pure barium titanate as filler,the dielectric constant of the composite modified by KH550 was improved and the dielectric loss was reduced.The dielectric foam prepared on this basis has stable dielectric constant（1.6）and low loss tangent(10^-3order of magnitude)when the filler content is 10vol%,but the density of the foam is slightly larger（0.265 g/cm³）due to the higher density of barium titanate.2、The polystyrene coating layer was synthesized on the surface of carbon nanotubes by atom transfer radical polymerization（ATRP）,and the obtained coated carbon nanotubes were physically blended with polypropylene to prepare composites.Polymer dielectric foam was prepared by physical foaming with carbon dioxide.The results show that polystyrene coating layer can effectively hinder the mutual contact between carbon nanotubes and reduce the leakage current of the material.Compared with pure carbon nanotubes as fillers,the barrier effect of polystyrene reduces the dielectric loss of the material,improves the percolation threshold of the material,and broadens the control window of the dielectric properties.At the same time,the nano-capacitance network formed between carbon nanotubes provides high dielectric constant for the composites.When the filler content was6.51 wt%,the prepared dielectric foam had stable dielectric constant（2.02）,low loss tangent(10^-3order of magnitude)and low density（0.091 g/cm³）.3、Silver nanoparticles modified carbon nanotubes were prepared by redox method,and the obtained modified carbon nanotubes were physically blended with polypropylene to prepare composites.Polymer dielectric foam was prepared by physical foaming with carbon dioxide.The results show that the coulomb blockade effect of silver nanoparticles can effectively limit the charge transfer in the material and reduce the dielectric loss of the material.At the same time,the nano-capacitance network formed between carbon nanotubes provides a high dielectric constant for the composite.The dielectric foam prepared on this basis has stable dielectric constant（1.91）and low density（0.073 g/cm³）when the filler content is 6.51 wt%.However,due to the existence of some conductive pathways in the material,the loss angle tangent is slightly larger(10^-2order of magnitude).